Touch sensitive capacitor timing percussion keying circuit



Apr-i121, 1970 L.DE PREE 3,507,973 TOUCH SENSITIVE CAPACITOR TIMINGPERCUSSION'KEYING CIRCUIT Filed May 1, 1968 F/ G1 KEY SWITCHES X F/GZA'o PERCUSS/VE CIRCUIT 3,507,973 TOUCH SENSITIVE CAPACITOR TIMINGPERCUSSION KEYING CIRCUIT Lee De Pree, 17 E. 8th St, Holland, Mich.49423 Filed May 1, 1968, Ser. No. 725,614 Int. Cl. Gh 1/00, 1/02 US. Cl.84-1.24 2 Claims ABSTRACT OF THE DISCLOSURE In an electronic pianoforteor similar percussive musical instrument, a key operated switch inconjunction with a capacitor, for supplying a controlled amplitudevoltage pulse; the amplitude of the pulse dependent on the extent thecapacitor is discharged by the timed operation of the switch, prior tothe delivery of the pulse.

This invention relates to a key or button operated electrical switch foran electronic musical instrument wherein percussive tones are desired,and wherein the amplitude of the tone must be controlled by the speedwith which the key'is depressed, as in a pianoforte.

One method of producing a percussive tone electronically is to passelectric oscillations of constant frequency and amplitude in the audiofrequency range, to an electronic percussive keying circuit; saidcircut, when activated from a source of diminishing DC. voltage,transmitting the oscillations in gradually decreasing intensity untiltransmission stops; the strength of the transmitted signal beingproportional to the DC voltage applied to the circuit.

A touch sensitive, capacitor timing, key operated switch for anelectronic pianoforte, when used in conjunction with a percussivecircuit as above, must perform the following functions:

(1) Charge a capacitor from a suitable D.C. supply.

(2) Partially discharge capacitor by timed switching;

controlled by key velocity.

(3) Transmit remainder of charge to percussive circuitry.

(4) Terminate D.C. current flow when key is released.

Heretofore, to perform the above functions, a switch needed either aplurality of moveable elements, or resorted to the use of slidingcontacts. My invention embodies a simpler switch with one moveableelement which will perform the above functions. The advantage of theinvention will become more apparent upon reference to the followingspecification, in connection with the accompanying drawings in which:

FIGURE 1 is a block diagram showing the relationship of the switch toother elements in a typical electronic percussive circuit.

FIGURE 2A is a diagram of the key operated switch and actuator.

FIGURE 2B illustrates the operation of the switch by the moving andflexing of the moveable element.

In FIGURE 1, I show the flow of tones from source to audio outputthrough the percussive circuits when said circuits are activated byoperation of the key switches. FIGURE 2A is a diagram of a key switchand associated capacitor and resistor and a representation of a key 1and the attached actuator 2. The drawing shows the switch position withthe key at rest.

The key switch comprises a straight, moveable, elastic conductiveelement 3 and fixed conductive elements 4, 5, and 6. Element 3 may be.02 inch diameter Phosphor United States Patent 0 "Ice bronze springwire. The free end of element 3 is in contact with fixed element 4,which is connected to a suitable D.C. source, in this instance aboutplus 35 volts. Element 4 may be a Phosphor bronze wire buss supplyingall the switches. The fixed end of 3, which is connected to groundthrough resistor 7 and capacitor 8, is so located that the free end of 3contacts elements 6 before it contacts element 5 when the switch isoperated.

When the piano key is depressed, contact between 3 and 4 is broken, andelement 3 makes contact with element 6, a voltage decay buss, which maybe a Phosphor bronze wire, through which a portion of the charge incapacitor 8 is dissipated. Said buss, however, is connected to a lowvoltage D.C. supply, the voltage being barely suflicient to fire thekeying circuit; said voltage assures that although the piano key may bedepressed very slowly, sufficient voltage remains in capacitor 8 to firethe keying circuit and produce an audible tone.

FIG. 2B shows the effect of flexing element 3 by further movement ofactuator 2. As element 3 bears against 6, it flexes until contact ismade with element 5, which is connected to the keying circuitry of theindividual note being produced. Further flexing breaks contact at 6.

The duration of dwell of element 3 on 6 is determined by the speed withwhich the piano key is depressed. This in turn determines the amount ofcharge and resulting voltage remaining in capacitor 8, which in turndetermines the initial amplitude of the tone or signal passed throughthe keying circuit when it is fired through element 5.

The gradual discharge of capacitor 8, through element 5 and thepercussive circuit, results in a gradually diminishing audio tone. Thetone is terminated when the capacitor has discharged or when the key isreleased.

What I claim and desire to secure by Letters Patent of the United Statesis as follows:

1. An electrical switch, comprising a movable, elastic conductiveelement, one end of said element being fiexd, the moveable endcontacting in sequence a plurality of fixed conductive elements, thefixed elements being so arranged that the duration of dwell of themovable element on some of the fixed elements is controlled by the rateof flexing of the moveable element when bearing against other of thefixed elements.

2. The combination as defined in claim 1 wherein one of the fixedelements supplies DC. voltage to electrically charge a capacitor throughthe moveable element, and wherein another fixed element, carrying alower DC. voltage, serves to discharge the capacitor, the extent ofdischarge being dependent on the duration of dwell of the moveableelement on the latter fixed element, and the extent of discharge limitedby the electrical potential on the latter fixed element.

References Cited UNITED STATES PATENTS 2,482,548 9/1949 Kerkhof 84-1263,018,353 1/1962 Mitchell ZOO-166.1 3,259,728 7/ 1966 De Rougemont eta1.

3,306,969 2/1967 Barber 84-124 3,333,043 7/1967 Slaats et al 841.263,197,709 7/1965 Antonio et al. 307208 X HERMAN KARL SAALBACH, PrimaryExaminer M. NUSSBAUM, Assistant Examiner US. Cl. X.R. 84-1.27

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3507973Dated April 21 970 Lee De Pree Inventor(s) It is certified that errorappears in the above-identified patent and that said Letters Patent arehereby corrected as shown below:

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